The present invention relates to a still image pickup camera using a CCD solid state image pickup device of the frame transfer (FT) type or interline type and, more particularly, to a camera of this type for photographing an instantaneous still image of an object and outputting a still video signal indicative of the still image.
The CCD solid state image pickup device of the FT type comprises: an image pickup area (photo sensing area) to be exposed; a temporary storage area to temporarily store the signal charges transferred from the image pickup area; and a horizontal shift register to read out the video signal from the temporary storage area. Transfer electrodes are vertically arranged for those areas and shift register. The temporary storage area and shift register are shielded against light by a metal film or the like through a thin insulating film.
Prior to photographing an object, first high-speed transfer pulses as many as the number of pixels in the vertical direction are given for the vertical blanking period, the signal charges of one field of the image pickup area are transferred to the temporary storage area to clear the image pickup area. Thus, the storage of the signal charges of the next one field is started in the image pickup area. In the image pickup area, the storage of the signal charges of one field is continued until the next vertical sync signal appears. Namely, the storage interval of the signal charges is equal to one field interval and is 1/60 seconds (.apprxeq.16.7 msec).
In the one field interval when the signal charges are stored in the image pickup area, the second transfer pulse is given to the temporary storage area every horizontal sync signal. The signal charges transferred from the image pickup area to the temporary storage area are transferred to the horizontal shift register. Namely, the image data of one horizontal line is transferred to the horizontal shift register in response to one second transfer pulse.
The image data of one horizontal line transferred to the horizontal shift register is output to the outside every pixel data in response to every input of one third transfer pulse. Since the third transfer pulses of the number larger than the number of pixels of one horizontal line are given for one horizontal scan period, all of the image data of one horizontal line is output as a video signal output to the outside within one horizontal scan period from the input of the preceding horizontal sync signal to the input of the next horizontal sync signal. In one field interval, all image data of one field which has already been stored in the temporary storage area is output as a serial video signal.
The storage interval of the signal charges in the image pickup area is equal to one field interval and is constant. This one field interval corresponds to the shutter speed. In this case, it is the fixed shutter speed (1/60 sec). Therefore, in the case of a moving object, an instantaneous moving object cannot be photographed as a still image, causing an inconvenience in that the photographed image is slightly blurred.
Hitherto, the following methods have been used in order to enable a storage interval corresponding to the shutter speed of, e.g., 1/500 sec or 1/1000 sec to be obtained in accordance with the moving speed of a moving object.
(1) A mechanical shutter is provided between the photographing lenses and the CCD solid state image pickup device.
(2) An electronic shutter constituted by a PLZT which mainly consists of the components of Pb, La, Zr, and Ti is provided.
(3) A stroboscopic flash is used.
(4) The CCD solid state image pickup device is scanned at a high speed.
However, these methods have the following problems, respectively.
In the case of the mechanical shutter, the life is short, the structure is complicated, and it is difficult to reduce the size and cost. In the case of the PLZT electronic shutter, the light amount remarkably decreases because the polarized light is used and, on the other hand, a pulse voltage of hundreds of volts is needed as a voltage to be applied to the shutter. The stroboscopic flash is expensive and can be used only under a dark circumferential condition, so that the use condition is limited and the flash light gives an unpleasant feeling to the person to be photographed. In the case of scanning the CCD solid state image pickup device at a high speed, the peripheral circuits must be also made operative at a high speed and such a high-speed operation is technically difficult.